1. Field of the Invention
The present invention relates to double-sided emissive liquid crystal display (LCD) modules, and more particularly, a double-sided emissive LCD module enabling effective use of light from a backlight.
2. Description of the Related Art
In recent years, portable information terminals, such as cellular phones, personal digital assistants, and portable terminals with a cellular phone function and the capability of displaying a large number of messages, have become widely available. Portable information terminals often use transflective LCDs to save power. Under bright lighting conditions the transflective LCDs operate in a reflective mode, while under poor lighting conditions they operate using backlights, frontlights, and so on.
Among portable, information terminals, cellular phones usually have a primary display for displaying various information such as transmitted and received messages on the front face of a housing. Recently, a cellular phone that has an auxiliary display on the back face of the housing has become commercially available.
FIGS. 6A and 6B show external views of such a cellular phone. A cellular phone 301 consists of an upper housing 301a and a lower housing 301b that are connected with a hinge 301c enabling the phone to open and close freely. A double-sided emissive LCD module is built into the upper housing 301a and is composed of a primary display unit and an auxiliary display unit. The primary display unit has a primary display 301e exposed on an operation side 301d of the phone. The auxiliary display unit has an auxiliary display 301h exposed on a back housing 301g. 
An operating side 301j on the lower housing 301b has a keyboard 301k for dialing and other operations.
FIG. 7 shows the detailed structure of the double-sided emissive LCD module. The double-sided emissive LCD module 302 is composed of a primary display unit 303 including the primary display 301e and an auxiliary display unit 304 having the auxiliary display 301h. The primary display unit 303 is composed of a transflective LCD panel 303a (hereinafter called a primary display panel) and a primary backlight 303b for illuminating the primary display panel 303a. The primary backlight 303b is composed of a light source 303c and a light guide plate 303d. 
The auxiliary display unit 304 is composed of a transflective LCD panel 304a (hereinafter called an auxiliary display panel) smaller than the primary display panel 303a and an auxiliary backlight 304b for illuminating the auxiliary display panel 304a. The auxiliary backlight 304b is composed of a light source 304c and a light guide plate 304d. 
The primary backlight 303b is larger than the auxiliary backlight 304b, but both of them consist of almost the same components (light sources 303c and 304c, and light guide plates 303d and 304d).
Even when the upper housing 301a and the lower housing 301b are folded together via the hinge 301c, the auxiliary display 301h is on the back of the upper housing 301a. Thus, various information of the cellular phone 301 can be seen without opening the upper housing 301a and the lower housing 301b. 
However, the known cellular phone 301 has both the primary backlight 303b and the auxiliary backlight 304b. This has the drawback of requiring a large number of parts and a complicated internal structure, thus resulting in a thicker product.
In view of the fact that the primary backlight 303b and the auxiliary backlight 304b are composed of the same kind of components, a single backlight which combines the backlights for the primary display unit and the auxiliary display unit is disclosed in Japanese Unexamined Patent Application Publication No. 2000-338483.